Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-04-02
2003-09-09
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C428S213000, C428S214000, C428S215000, C428S343000, C428S346000, C428S347000, C428S349000, C428S3550EN, C428S3550AC, C428S480000, C428S483000, C525S437000, C525S447000, C525S449000, C525S450000, C525S451000
Reexamination Certificate
active
06616998
ABSTRACT:
TECHNICAL FIELD
This invention relates to a heat sealable polyester packaging film producing a peelable seal when heat sealed to itself and other polyester materials, and more particularly this invention relates to multi-layer packaging structures having at least one layer of the film of the invention.
BACKGROUND OF THE INVENTION
Polyesters are commonly used in the packaging of a wide range of foods, beverages, industrial articles, medicinal products and the like. For example, poly (ethylene terephthalate) (PET) polyesters are used in the form of bottles, film, sheeting, thermoformed articles and the like for various packaging applications.
In many of these types of applications, consumers desire to have a readily peelable seal to enable easy access to the contents of a package. Peelable seals are those that have a mechanical strength which is, at the same time, sufficiently high to keep the package intact until it has to be opened by the consumer and sufficiently low to enable manual opening of the package without the use of any auxiliary instrument.
In the forming of peelable seals during the enclosure of an article in a package, manufacturers prefer a packaging material that is readily heat sealable to itself or another surface without the use of adhesives. Additionally, packaging materials capable of low temperature sealing are desirous to prevent damage of the articles or the packaging material itself.
Polyesters, while known to be heat sealable, are not capable of producing peelable seals. For films made of amorphous PET and PET copolyesters containing 1,4-cyclohexanedimethanol (CHDM), destructive film tear occurs when attempts are made to pull apart the seal. This type of bond failure is unacceptable for many packaging applications. Heat sealing of amorphous PET film to itself frequently causes crystallization of the PET. This leads to brittle bonds which are not useful for most packaging applications. Crystallized PET films, while heat sealable, are susceptible to having many processing difficulties and must be heat sealed at undesirably high temperatures in excess of 260° C. Again destructive tearing is observed when these sealed films are pulled apart.
Thus, there exists a need in the art for polyester packaging films which are easily heat sealed at relatively low temperatures to produce peelable seals without destructive bond failure. Accordingly, it is to the provision of such that the present invention is primarily directed.
BRIEF SUMMARY OF THE INVENTION
The present invention is a heat sealable packaging film, which produces a peelable seal. The film is formed from a blend of 99 to 75 weight percent of a copolyester and 1 to 25 weight percent of an epoxy-containing impact modifying polymer or a maleic anhydride-containing polymer.
The copolyester comprises diacid residues of at least 50 mole percent terephthalic acid, naphthalenedicarboxylic acid, 1,4-cyclohexane-dicarboxylic acid, or mixtures thereof and diol residues of about 90 to 35 mole percent ethylene glycol and 10 to 65 mole percent of at least one of diethylene glycol or 1,4-cyclohexanedimethanol. The diacid residues and the diol residues are each based on 100 mole percent.
The impact modifying polymer comprises about 0.5 to 20 weight percent of epoxy-containing monomers selected from glycidyl methacrylate, glycidyl acrylate, allyl glycidyl ether, 3,4-epoxy-1-butene, or a mixture thereof of any two or more monomers.
The maleic anhydride-containing polymer is selected from (i) a copolymer comprising about 80 to about 99 weight percent ethylene and about 1 to about 20 weight percent maleic anhydride, (ii) a grafted copolymer comprising about 1 to about 20 weight percent maleic anhydride and about 80 to about 99 weight percent olefin polymers, or (iii) a terpolymer comprising about 50 to about 98 weight percent ethylene, about 1 to about 20 weight percent maleic anhydride, and about 1 to about 30 weight percent alkyl acrylate.
DETAILED DESCRIPTION
Heat sealable packaging films that form a peelable seal can be made from a blend of (A) certain copolyesters and (B) epoxy-containing impact modifying polymers or maleic anhydride-containing polymers. Upon extrusion, the blends provide clear films and sheeting that are readily heat sealed to provide peelable bonds.
Heat sealing is conducted in a temperature range of about 85 to about 200° C. The preferred heat sealing range is about 100 to about 150° C. Sealing dwell times of about 0.5 to about 7 seconds are suitable. The heat sealable packaging film may be bonded to itself or to other polyester film or sheeting using conventional heat sealing methods. Other methods of heating the packaging film to an appropriate bonding temperature may also be used such as impulse heating, induction heating, infrared heating, radio frequency heating and the like.
The copolyester is present in the blend from about 99 to about 75 weight percent, based on the total weight of the components A and B. The copolyester comprises diacid residues of at least about 50 mole percent, preferably 80 mole percent, terephthalic acid, naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid or mixtures thereof. The copolyester comprises diol residues of about 90 to about 35 mole percent ethylene glycol and about 10 to about 65 mole percent of at least one of diethylene glycol or 1,4-cyclohexanedimethanol. The diacid residues and the diol residues are each based on 100 mole percent.
Mixtures of two or more dibasic acids and two or more glycols may be used if desired. Modifying amounts of dibasic acids containing from about four to about forty carbon atoms may be used including succinic, azelaic, adipic, sebacic, suberic, isophthalic, sulfoisophthalic, dimer and the like. Modifying amounts of glycols containing three to about ten carbon atoms may be used including propylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexane-dimethanol, 1,3-propanediol and the like.
The copolyesters are commercially available and/or may be prepared by batch or continuous processes using conventional melt phase or solid state condensation procedures well known in the art. Also, the polyester component may be obtained from post consumer waste, e.g., recycled polyester.
In preparing the copolyesters, the dibasic acid moiety may be derived from the acid, the acid chloride, or the lower alkyl esters. Any of the various isomers or mixtures of isomers of naphthalenedicarboxylic acid may be used but the 1,4-, 1,5-, 2,6-, and 2,7-isomers are preferred. Also cis, trans, or cis/trans mixtures of 1,4-cyclohexanedimethanol or of 1,4-cyclohexanedicarboxylic acid may be used.
The copolyesters of this invention will generally have inherent viscosity (I.V.) values in the range of about 0.4 to about 1.5, preferably 0.5 to about 1.0. I.V. is measured at 25° C. by dissolving 0.5 grams of polyester into 100 mL of a solvent mixture consisting of 60 percent by weight phenol and 40 percent by weight tetrachloroethane.
Typical additives for polyesters may be used if desired. Such additives include stabilizers, antioxidants, colorants, pigments, mold release agents, slip agents, carbon black, flame retardants and the like.
The epoxy-containing impact modifying polymers or maleic anhydride-containing polymers are present in the blend from about 1 to about 25 weight %, preferably about 2 to about 10 weight %, based on the total weight of the components A and B.
The impact modifying polymers are comprised of about 0.5 to 20 weight percent of epoxy-containing monomers selected from glycidyl methacrylate, glycidyl acrylate, allyl glycidyl ether, 3,4-epoxy-1-butene, or a mixture of any two or more of such monomers. The impact modifying polymers may be prepared either by copolymerization or grafting.
In the former preparation, the epoxy-containing monomers above are copolymerized with other monomers such as ethylene and, optionally alkyl acrylates. Such epoxy-containing impact modifying polymers are well known in the art and are available from a plurality of manufacturers.
In the latter preparation, g
George Scott Ellery
Greer Kathleen Diane
McConnell Richard Leon
Moolenaar Hubertus Jacobus Wilhelmus
Rhein James Edward
Boshears B. J.
Chen Vivian
Eastman Chemical Company
Graves Bernie
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